Influence of molecular weight on the phase behavior and structure formation of branched side-chain hairy-rod polyfluorene in bulk phase.

We report on an experimental study of the self-organization and phase behavior of hairy-rod π -conjugated branched side-chain polyfluorene, poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl]—i.e., poly[2,7–(9,9–bis(2–ethylhexyl)fluorene] (PF2∕6) —as a function of molecular weight (Mn) . The results have been compared to those of phenomenological theory. Samples for which Mn=3–147 kg∕mol were used. First, the stiffness of PF2∕6 , the assumption of the theory, has been probed by small-angle neutron scattering in solution. Thermogravimetry has been used to show that PF2∕6 is thermally stable over the conditions studied. Second, the existence of nematic and hexagonal phases has been phenomenologically identified for lower and higher Mn (LMW, Mn<Mn* and HMW, Mn>Mn* ) regimes, respectively, based on free-energy argument of nematic and hexagonal hairy rods and found to correspond to the experimental x-ray diffraction (XRD) results for PF2∕6 . By using the lattice parameters of PF2∕6 as an experimental input, the nematic-hexagonal transition has been predicted in the vicinity of glassification temperature (Tg) of PF2∕6 . Then, by taking the orientation parts of the free energies into account the nematic-hexagonal transition has been calculated as a function of temperature and Mn and a phase diagram has been formed. Below Tg of 80 °C only (frozen) nematic phase is observed for Mn<Mn*=104 g∕mol and crystalline hexagonal phase for Mn>Mn* . The nematic-hexagonal transition upon heating is observed for the HMW regime depending weakly on Mn , being at 140–165 °C for Mn>Mn* . Third, the phase behavior and structure formation as a function of Mn have been probed using powder and fiber XRD and differential scanning calorimetry and reasonable semiquantitative agreement with theory has been found for Mn≥3 kg∕mol . Fourth, structural characteristics are widely discussed. The nematic phase of LMW materials has been observed to be denser than high-temperature nematic phase of HMW compounds. The hexagonal phase has been found to be paracrystalline in the (ab0) plane but a genuine crystal meridionally. We also find that all these materials including the shortest 10-mer possess the formerly observed rigid five-helix hairy-rod molecular structure

Hamlet and the fall of the Berlin wall : the myth of interventionist Shakespeare performance

The critical reception of Heiner Müller’s 1990 Hamlet/Maschine at the Deutsches Theater in East Berlin epitomizes a trend of crediting GDR Shakespeare performance with political influence. Drawing on rehearsal notes and reviews, Oliver challenges the interventionist Shakespeare myth, contrasting the Deutsches Theater’s political involvement with the impact of its Hamlet production on events surrounding the fall of the Berlin Wall. Shakespeare’s capacity for political intervention at this point was limited by theater practitioners’ reliance on public funding, their close relationships with governmental authority, and an underlying distrust of the masses. Ultimately, GDR artists proved useful to the 1989 protest movement because they occupied a unique position at the interface of dissidence and power

Parameter interdependence and uncertainty induced by lumping in a hydrologic model

Throughout the world, watershed modeling is undertaken using lumped parameter hydrologic models that represent real-world processes in a manner that is at once abstract, but nevertheless relies on algorithms that reflect real-world processes and parameters that reflect real-world hydraulic properties. In most cases, values are assigned to the parameters of such models through calibration against flows at watershed outlets. One criterion by which the utility of the model and the success of the calibration process are judged is that realistic values are assigned to parameters through this process. This study employs regularization theory to examine the relationship between lumped parameters and corresponding real-world hydraulic properties. It demonstrates that any kind of parameter lumping or averaging can induce a substantial amount of ‘structural noise’ which devices such as Box-Cox transformation of flows and auto-regressive moving average (ARMA) modeling of residuals are unlikely to render homoscedastic and uncorrelated. Furthermore, values estimated for lumped parameters are unlikely to represent average values of the hydraulic properties after which they are named and are often contaminated to a greater or lesser degree by the values of hydraulic properties which they do not purport to represent at all. As a result, the question of how rigidly they should be bounded during the parameter estimation process is still an open one

On the polarization of the green emission of polyfluorenes

© 2003 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.1605374DOI: 10.1063/1.1605374An experimental and theoretical study of the anisotropic optical properties of polyfluorenes (PFs) bearing ketonic defects is presented. Polarized emission experiments performed on photooxidized aligned PF layers indicate that the transition dipole of the ‘‘green’’ CT π-π * transition of the keto-defect is oriented parallel to the chain direction. It is further observed that the polarization ratio of the green emission is slightly smaller than that of the blue emission component originating from undisturbed chains. Quantum mechanical calculations have been performed to support these observations. It is shown that the transition dipole moment of the CT π-π * transition of the defect is slightly misaligned with respect to the π-π* transition of the undisturbed PF chain, and that the angle between both depends on the chain conformation. For the most probably 5/2 helical conformation, this angle is, however, smaller than 5°. Further, polarized PL spectroscopy with polarized excitation has been performed to determine the extent of energy migration prior to emission from the keto-defect. For excitation at 380 nm, the polarization ratio of the green emission is essentially independent of the excitation polarization, indicating almost complete depolarization of the excitation before it is captured at a defect site. In contrast to this, energy migration after direct excitation of the keto-defect is inefficient or even absent

Electrophosphorescence And Delayed Electroluminescence From Pristine Polyfluorene Thin-film Devices At Low Temperature

Intrinsic long-lived electrophosphorescence and delayed electroluminescence from a conjugated polymer (polyfluorene) thin film is observed for the first time at low temperature. From bias offset voltage dependent measurements, it is concluded that the delayed fluorescence is generated via triplet-triplet annihilation. A fast and efficient triplet exciton quenching by charge carriers is found to occur in the active polymer layer of the working devices

Problèmes aux limites issus de la supraconductivité (estimations semi-classiques et comportement asymptotique des solutions)

Cette thèse est consacrèe à l'étude de plusieurs modèles de l'effet de proximité' dans le cadre de la thèorie de Ginzburg-Landau de la supraconductivité. Ces modèles proviennent des interfaces entre des supraconducteurs et des métaux normaux.Dans une première partie de cette thèse, nous estimons dans le régime semiclassique le bas du spectre d'un opérateur de Schrôdinger magnétique associé à une condition au bord du type Fourier (Robin), appelée dans ce contexte la condition au bord de de Gennes, et nous étudions également la localisation des états fondamentaux. Nous exhibons des cas où la condition au bord de de Gennes a des effets forts sur cette localisation.Dans une autre partie, nous construisons un problème spectral lié à l'apparition de la supraconductivité pour une fonctionnelle de Ginzburg-Landau généralisée ayant des coefficients discontinues, où le paramètre d'ordre' et le potentiel magnétique' sont définis dans l'espace entier. Pourle régime où le paramétre de Ginzburg-Landau est grand, nous estimons le champ surcritique corespondant au champ pour lequel les états normaux perdent leur stabilité. Dans d'autres régimes asymptotiques, nous retrouvons un développement limité déjà obtenu pour un autre modèle standard'.Dans la dernière partie, nous étudions de nouveau une fonctionnelle de Ginzburg-Landau généralisée mais dans le cas sans champ magnétique appliqué. Nous obtenons dans ce cas le comportement asymptotique du paramètre d'ordre pour le régime où le paramètre de Ginzburg-Landau est grand. Ceci montre en particulier que la supraconductivité persiste dans une bande mince dans le métal normal, près du bord du supraconducteur.This thesis is devoted to the study of various models for the proximity effect' in the frame work of the Ginzburg-Landau theory of superconductivity. These models arise in the situation when a superconductor is adjacent to a normal metal.In a first part of this thesis, we estimate in the semi-classical limit the ground state energy of a magnetic Schrôdinger operator associated to a Fourier (Robin) type boundary condition, called in this context the de Gennes boundary condition, and we study the localization of the ground states. We exhibit cases when the de Gennes boundary condition has strong effects on this localization.In another part, we formulate a spectral problem related to the onset of superconductivity for a generalized Ginzburg-Landau functional having discontinuous coefficients, where the order parameter and the magnetic potential are defined in the whole space In the regime when the Ginzburg-Landau parameter (of the superconducting material) is large, we estimate the critical applied magnetic field for which the normal state will lose its stability. In some asymptotic situations, we recover results related to the standard' Ginzburg-Landau model.In the final part, we study again a generalized Ginzburg-Landau functional in the case without an applied magnetic field. We determine in this case the asymptotic behavior of the order parameter in the regime when the Ginzburg-Landau parameter is large. This shows in particular that the superconductivity persists in a thin boundary sheath of the normal material, near the boundary of the superconductor.ORSAY-PARIS 11-BU Sciences (914712101) / SudocORSAY-PARIS 11-Bib. Maths (914712203) / SudocSudocFranceF

Surface freshwater storage and variability in the Amazon basin from multi-satellite observations, 1993-2007

The amount of water stored and moving through the surface water bodies of large river basins (river, floodplains, wetlands) plays a major role in the global water and biochemical cycles and is a critical parameter for water resources management. However, the spatiotemporal variations of these freshwater reservoirs are still widely unknown at the global scale. Here, we propose a hypsographic curve approach to estimate surface freshwater storage variations over the Amazon basin combining surface water extent from a multi-satellite-technique with topographic data from the Global Digital Elevation Model (GDEM) from Advance Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Monthly surface water storage variations for 1993-2007 are presented, showing a strong seasonal and interannual variability, and are evaluated against in situ river discharge and precipitation. The basin-scale mean annual amplitude of similar to 1200 km(3) is in the range of previous estimates and contributes to about half of the Gravity Recovery And Climate Experiment (GRACE) total water storage variations. For the first time, we map the surface water volume anomaly during the extreme droughts of 1997 (October-November) and 2005 (September-October) and found that during these dry events the water stored in the river and floodplains of the Amazon basin was, respectively, similar to 230 (similar to 40%) and 210 (similar to 50%) km(3) below the 1993-2007 average. This new 15 year data set of surface water volume represents an unprecedented source of information for future hydrological or climate modeling of the Amazon. It is also a first step toward the development of such database at the global scale

Heart failure in patients with coronary heart disease: Prevalence, characteristics and guideline implementation – Results from the German EuroAspire IV cohort

Background: Adherence to pharmacotherapeutic treatment guidelines in patients with heart failure (HF) is of major prognostic importance, but thorough implementation of guidelines in routine care remains insufficient. Our aim was to investigate prevalence and characteristics of HF in patients with coronary heart disease (CHD), and to assess the adherence to current HF guidelines in patients with HF stage C, thus identifying potential targets for the optimization of guideline implementation. Methods: Patients from the German sample of the European Action on Secondary and Primary Prevention by Intervention to Reduce Events (EuroAspire) IV survey with a hospitalization for CHD within the previous six to 36 months providing valid data on echocardiography as well as on signs and symptoms of HF were categorized into stages of HF: A, prevalence of risk factors for developing HF; B, asymptomatic but with structural heart disease; C, symptomatic HF. A Guideline Adherence Indicator (GAI-3) was calculated for patients with reduced (≤40%) left ventricular ejection fraction (HFrEF) as number of drugs taken per number of drugs indicated; beta-blockers, angiotensin converting enzyme inhibitors/angiotensin receptor blockers, and mineralocorticoid receptor antagonists (MRA) were considered. Results: 509/536 patients entered analysis. HF stage A was prevalent in n = 20 (3.9%), stage B in n = 264 (51.9%), and stage C in n = 225 (44.2%) patients; 94/225 patients were diagnosed with HFrEF (42%). Stage C patients were older, had a longer duration of CHD, and a higher prevalence of arterial hypertension. Awareness of pre-diagnosed HF was low (19%). Overall GAI-3 of HFrEF patients was 96.4% with a trend towards lower GAI-3 in patients with lower LVEF due to less thorough MRA prescription. Conclusions: In our sample of CHD patients, prevalence of HF stage C was high and a sizable subgroup suffered from HFrEF. Overall, pharmacotherapy was fairly well implemented in HFrEF patients, although somewhat worse in patients with more reduced ejection fraction. Two major targets were identified possibly suited to further improve the implementation of HF guidelines: 1) increase patients´ awareness of diagnosis and importance of HF; and 2) disseminate knowledge about the importance of appropriately implementing the use of mineralocorticoid receptor antagonist